The first basic law of human stupidity asserts without ambiguity that:

Always and inevitably everyone underestimates the number of stupid individuals in circulation.

At first, the statement sounds trivial, vague and horribly ungenerous. Closer scrutiny will however reveal its realistic veracity. No matter how high are one's estimates of human stupidity, one is repeatedly and recurrently startled by the fact that:

a) people whom one had once judged rational and intelligent turn out to be unashamedly stupid.

b) day after day, with unceasing monotony, one is harassed in one's activities by stupid individuals who appear suddenly and unexpectedly in the most inconvenient places and at the most improbable moments.

Update: Prof. Cipolla retired from UCB in 1991, and died on September 5, 2000, in Pavia, Italy. Unfortunately, his former publisher has demanded that his writing be effaced from the WWW, threatening lawsuits. While the work is in the public domain, and cannot be retracted, defending that would cost.